Golden Alga (Prymnesium parvum) in Texas

Workshop Abstracts


Bloom Control Strategies for Harmful Algal Blooms.

Don Anderson speaking at Golden Alga Workshop Donald M. Anderson* and Mario R. Sengco

Biology Department, Woods Hole Oceanographic Institution, Woods Hole, MA 02543 USA

Abstract.--Efforts to manage harmful algal blooms (HABs) throughout the world have focused mainly on their prevention, and the mitigation of their impacts on public health, fisheries, and important aquaculture industries. While critical and effective, such management programs only address the apparent "symptoms" of HABs without dealing with the causative organisms directly. Currently, there are few strategies to control an existing or persistent outbreak that threatens coastal resources. Bloom control strategies have included the use of ozone and various algicidal chemicals (e.g. copper sulfate, barley straw). Ultrasonic devices induce species-specific algal lysis in small volumes (e.g. ponds and aquaria), but have not been fully explored for use in large-scale brackish or marine systems. The biological control of HABs – through the introduction of algal pathogens (i.e. viruses, bacteria), parasites, competitors and grazers – has been proposed, but not yet attempted at meaningful scales. Chemicals such as alum and a wide assortment of organic flocculants have been tested to determine whether blooms can be removed from the water column by promoting algal flocculation and rapid settling. In marine systems, attempts to use chemical flocculants have been reported in Asia, although results were limited due to rapid dilution and high cost. A variant to this chemical-flocculation approach is the addition of clay minerals to HABs to flocculate and settle the organisms directly. Essentially, these minute (< 2 µm), but dense minerals bind and act to ballast the organisms to promote cell sinking, despite the organisms’ motility and buoyancy. Underlying cells are further removed by entrainment into the settling aggregates. The high removal efficiency, rapidity, cost effectiveness and low environmental impacts of clay dispersal have made it one of the most promising control methods under investigation. The potential use of clays to control harmful algal blooms (HABs) has been explored in Japan, South Korea, China, Australia, the United States, and Sweden. In Japan and South Korea, minerals such as montmorillonite, kaolinite, and yellow loess, have already been used in the field effectively, to protect fish mariculture from Cochlodinium spp. and other blooms. In the U.S., several clays and clay-rich sediments have shown high removal abilities (e.g. > 80% cell removal efficiency) against Karenia brevis, Heterosigma akashiwo, Pfiesteria piscicida and Aureococcus anophagefferens. Benthic impact studies in the laboratory, and early studies in the field, have revealed some repercussion on survival and growth of certain species, and on the composition and abundance of benthic communities. However, these impacts have to be interpreted in the proper context to evaluate the acceptability of the clay control method. In Sweden, phosphatic clay (at 4 g/L) can remove up to 100% of Prymnesium parvum, but cell removal was influenced by cell concentration and physiology (N- or P- deficiency). Initial experiments with European clays showed promise through the use of raw, unincinerated clay and the addition of polyaluminum chloride (PAC) to enhance clay adhesiveness. A related mitigation method uses a proprietary clay formulation to scavenge phosphorus from freshwater systems, and to “lock” phosphorus in bottom sediments through the formation of a relatively impervious clay layer at the sediment surface. This technology will be described and discussed in the context of its possible utility during P. parvum blooms. The potential control of P. parvum with clay will be discussed, emphasizing the challenges of applying control methodologies developed from marine HABs to a low salinity environment.

*Presenter at Golden Alga Workshop

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